She recounted her shocking experience on a British Transport Police video.

She said she was travelling alone on the underground train at around 11.30pm when Firah got on and sat directly opposite her.

“I realised something was amiss when he looked at me and was smiling at me really intensely,” she said.

“At first I thought he was just a bit over friendly, but he didn’t break his focus the whole time - that was when I started feeling a little bit uncomfortable.”

He got off at the same station as Jessica and followed her through the tunnel, touching her inappropriately and saying things like “You’ve got a very innocent face.”

“I was a bit shocked,” she said. “He carried on talking to me, continued to keep putting his hand on and off my bottom.

'I just couldn’t believe it was happening'

“We went up the escalator and I tried to think of some action plan. I looked behind me and he was right behind me.

“He wedged himself beside me and had his hand on my bottom for the entire journey up the escalator

“I just remember thinking I need to get out of this station. I just couldn’t believe it was happening”

Jessica told The Gazette the incident has not stopped her from using the underground late at night.

“Now I know it might happen I keep my wits about me,” she said.

Firah was caught in May after the investigation led officers to CCTV that found him regularly travelling to Balham.

Detective Constable Allan McTaggart said: “This man sexually assaulted another passenger and I am pleased the courts recognised the severity of his actions which were totally unacceptable.

“Nobody should fear using public transport, and we are committed to making the rail network a safe place for passengers and a hostile environment for potential sex offenders.

Firah was also put on the sex offenders register for seven years and made the subject of a sexual harm prevention order. He will be required to have a registered Oyster card for the next three years when travelling on the London Underground network.